Electrolytic method of producing titanium



United States Patent ELECTROLYTIC Maroon 0F PRODUCING TITANIUM EugeneWainer, Qleveland Heights, Ohio, assignor, by rnesne assignments, toHorizons Titanium Corporation, Princeton, N. 3., a corporation of NewJersey No Drawing. Application May 16, 1956 Serial No. 585,172

7 Claims. (Cl. 204-64) This invention relates to the production of lowervalent halides of certain polyvalent transition metals from which themetals themselves may be obtained either by subsequentdisproportionation of the lower valent metal halide or by electrolyticdecomposition of the lower valent metal halide while dissolved in orassimilated by a fused salt bath.

Because of the possibilities inherent in the production of varioustransition metals either by electrolytic decomposition or bydisproportionation of their lower valent halides, considerable attentionhas been devoted heretofore to the production of these lower valenthalides. For this purpose, numerous reducing agents such as hydrogen andvarious metals have been proposed and used, but it has beencharacteristic of such procedures that a significant portion of thehalogen component of the initial transition metal halide has been lostby its combination with the reducing agent. Consequently, the amount oflower valent transition metal halide thus produced has always been lessthan the starting amount of the higher valent transition metal halide.The use of the transition metal itself as a reducing agent has beenproposed and explored but the inherent disadvantage in this procedure isthat it is predicated upon the previous'production of the transitionmetal itself.

I have now discovered that the lower valent halides of the multivalenttransition metals: titanium, zirconium, hafnium, vanadium, niobium andtantalu'mmay be obtained by reaction between the higher valent simplehalides of the metals and the lower valent sulfides of these metals. Themethod of my invention for producing the lower valent halides of thesemetals comprises bringing the higher valent simple halide of the metalin the vapor state into contact with a mass of the lower valent sulfideof one of these metals in the form of particles at-least as fine asabout 200mesh, and efiecting reaction between the highervalent metalhalide and the lower valent sulfide by maintaining the reactants at atemperature at least as high as the volatilization temperature of thehigher valentmetal halide but below that at which the resulting lowervalent metal halide disproportionates to the metal itself. I havefurther discovered that if the resulting lower valent transition metalhalide is supplied to a suitable fused salt bath and is subjected to anelectrolysis therein, the combination of these steps results in aprocess wherein the transition metal sulfide is converted to thetransition metal itself without consumption of the transition metalhigher valent halide.

The higher valent halides of the aforementioned transition metalsusefulin practicing the invention comprise the simple chlorides, bromides,iodides or fluorides provided that they are sufliciently volatile topermit their reaction with the lower valent sulfide in the substantiallydry state, i. e., in the substantial absence of .a molten phase attemperatures below those at which the corresponding lower valent halidedisproportionates. In general, these higher valent halides which arereadily volatile are the tetra 2,833,70fi Patented May 6, 1958 "tee a;(in

valent halides, although in the case of vanadium, higher valent halidessuch as the pentavalent halides are available. All of these metalhalides are available in a state of purity adequate for the practice ofmy invention, but if desired, these halides maybe further purified bydistilling or subliming them into the reaction zone, or by any otherappropriate purification procedure.

The transition metal sulfide used in, the practice of my inventionshould be of high purity; that is, it should be free of contaminantswhich would otherwise be carried over into the lower valent halideproduct. High purity transition metal sulfides can be produced either byreacting the transition metal halides with hydrogen sulfide atappropriate elevated temperatures or by heating the impure transitionmetal with elemental sulfur under a controlled atmosphere. In the eventthat the metal is one which combines to form more than one sulfide, thetransition metal sulfide selected should be one in which the transitionmetal exhibits a lower valence than the maximum valence of thetransition metal. For example, in the case of titanium, three sulfidesare known, namely, titanium disulfide, titanium sesquisulfide, andtitanium monosulfide. In the practice of my invention only the lattertwo sulfides may be used, and where a divalent titanium halide is to beobtained, only the divalent sulfide, titanium monosulfide can be used.

In general, whatever the transition metal sulfide employed, it should bechosen from sulfides in which the valence of the transition metal is nohigher than the valence of the transition metal in the lower valenttransition metal halide to be produced. v

The transition metal sulfide should be in a finely divided form in orderto promote reaction between the sulfide and the transition metal highervalent halide. In general, I have found it advisable to use a sulfideparticle size at least as fine as about 200 mesh (Tyler Standard). Thereaction between the higher valent transition metal halide and thetransition metal sulfide takes place readily at elevated temperatureswhen the vapors of the halide are passed over or through a mass of thefinely divided sulfide. The reaction vessel, such as a quartz-linedfurnace, should be gas-tight so that its atmosphere may be evacuated,then flushed with an inert gas such as argon and finally reevacuatedprior to the introduction of the transition metal higher valent halide.The reaction vessel is also advantageously provided with an outletcommunicating with a closed condensing system in which the lower valenttransition metal halide product may be liquifiedor solidified if thereaction temperature is above the normally liquid or solid state of thelower valent halide product.

The reaction temperatures at which the lower valent halides of theaforementioned polyvalent transition metals may be produced by thepractice of my invention range between 300 and 1100 (3., although theoptimuiri temperature range for the production of the lower valenthalides of the individual transition metals generally encompasses anarrower temperature range within this overall temperature range. Ineach instance, the reaction temperature should be at least as high asthe volatilizaltion temperature of the higher valent metal halide butbelow that at which the resulting lower valent halide dispropor tionatesto the metal itself. Thus, effective reaction temperature ranges are asfollows:

C. Niobium About 400-900 Tantalum About 400-900 Titanium About 300-800Vanadium About 300-800 Zirconium About 600-1100 Hafnium About 600-1100Within each of these ranges, higher temperatures promote vantageously inthe reaction zone in order to promote more rapid rate of the conversionof the higher valent transition metal halide to the lower valent halide.

The lower valent transition metal halide produced by the practice of myinvention is generally the trivalent halide, although this halide isfrequently accompanied by other lower valent halides. Within theeffective operating temperature range for each transaction metal halide,lower temperatures tend to promote the formation of halides having alower valence than the halides produced at the higher operatingtemperatures. For example, in producing the lower halides of titaniumfrom the tetrahalides of titanium, titanium trihalide formation isfavored by reaction temperatures of about 400600 C.; but by lowering thetemperature below this normal operating range for these metal halides,that is, by using a temperature of about 200-350 C. at subatmosphericpressure, the dihalide predominates in the reaction product. Thus, byusing a temperature range near or even below the optimum temperatureranges set forth hereinbefore, and by further using subatmosphericpressures, the reaction may be made to proceed effectively with theproduction of the lowest valent halides of each polyvalent transitionmetal, although generally, this result is achieved at the expense oflower reaction efliciency.

The following examples are illustrative of the practice of my inventionfor the production of lower valent halides of the aforementionedtransition metals.

Example I A silica t'ube furnace, equipped with a vacuum-tight watercooled headwas used as the reactionvessel. A boatcontaining 200 grns. of200 mesh high purity titanium monosulfide was inserted in the furnaceand the unit was sealed and evacuated; The furnace was heated to atemperature of about 550 C. and titanium tetrachloride was thendistilledinto the reactor at a rate sufficient to maintain a reactionzone pressure of about one atmosphere. After four hours at 750 C., thefurnace was cooled while maintaining a titanium tetrachloride pressureof one atmosphere until the furnace temperature was below the normalboiling point of titanium tetrachloride. The furnace was then opened,and the reacted mass was removed and leached with aqueous 1 Nhydrochloric acid. After filtration, an aqueous solution of puretitanium trichloride was obtained.

Example ll I Example III The :reaction described in Example I wasconducted in a quartz lined bomb. Liquid titanium tetrabromide andtitanium monosulfide were sealed in the bomb, which was then heated to450 C. A mixture of titanium dibromide and tribromide was obtained.

4 Example IV 200 grams zirconium sulfide and zirconium tetrachloridewere reacted as described in Example I. The reaction temperature washeld at about 800 C. Substantially a yield of zirconium trichloride wasobtained (1950 grams).

The lower valent transition metal halides produced by the practice of myinvention may be used as a source of the transition metal supply forfused salt bath electrolytic production of the transition metal itselfwhich results in a process wherein the transition metal sulfide isconverted to the metallic state. The production of the lower valenthalides can be visualized by the following representative equations inwhich M represents the transition metal, X

represents a halogen and S is sulfur:

3MX +2MS 5MX +S X l) 8MX +2MS- l0MX +S X (2) Example V A boat containing200 grams of minus 200 mesh (Tyler. Standard) high purity titaniummonosulfide was inserted in asilica tube furnace equipped with a vacuumtight.

water cooled head; The furnace was sealed and evacuated. After thefurnace was brought up to a temperature of about 550 C. titaniumtetrachloride was admitted to the furnace reaction zone at a ratesufficient to maintain the pressure in the reaction zone at about oneatmosphere, and the temperature of the furnace was raised to about 750C. After four hours at 750 C., the furnace was cooled to about 100 C.while maintaining an atmosphere of titanium tetrachloride therein. Thesolid reacted mass was removed and leached with molten sodium chloride.Suificient sodium chloride was employed to dissolve substantially all ofthe titanium diand trichloride which formed and a melt containingupwards of about 93% by weight of sodium chloride was thereby produced.

The molten halide mixture was charged into an electrolytic cell providedwith the usual means known in the art for maintaining the desiredtemperature, pressure, and atmosphere in the cell. The electrolysis ofthe molten chloride bath Was carried out employing a graphite anode anda nickel cathode at a cell voltage of 1.6 volts and a cathode currentdensity of 100 amperes per squaredecimeter. A finely crystalline depositof metallic titanium was obtained on the cathode weighing 470 grams.Anal- ,ysis of the residue obtained by leaching of the reaction masswith NaCl indicated a metal recovery of 93% based on the initial TiS andthat the product was /3 TiCl and /3 TiCl Example VI The molten mixtureobtained by leaching the reaction 0 Example VII Example V wasrepeatedexcept that the electrolysis bath was prepared by leaching thereactionmass .of EX- ample IV with molten sodiumchloride. In the ensuingelectrolysis, 850 grams of the zirconium were recovered as a cathodedeposit. The electrolysis was carried out at 875 C., at 1.9 volts and100 amperes per square decimeter of cathode area. The metal yield was94.5%.

Although the practice of the invention has been described andillustrated herein'oefore for the production of transition metal and thesulfide of another transition '1;

metal, or by the useof either a mixture of the higher valent halides oftwo or more transition metals or of the sulfides of two or moretransition metals, or by a combination of these procedures. The finalmetallic product can therefore be either the substantially puretransition metal itself or a mixture of two or more of these metals.

Furthermore although the foregoing specification has exemplified thepreparation of lower valent halides of the several polyvalent transitionmetals by reaction between their simple higher valent halides (e. g.TiCl ZrCl VCl VB) and their simple sulfides, it is to be noted thatsimilar reactions may be effected between the simple sulfides and thecomplex higher valent halides of these metals, such as the doublehalides of the transition metal and an alkali metal, in which thetransition metal exhibits one of its higher valent states. Thus K TiClNa TiCl KgTiFs or Na TiF or other suitable complex tetrahalides oftitanium may be substituted for the TiCl of Examples I or II, withsimilar results. Or complex titanium-alkmi metal-bromides and complexzirconium halides in which the zirconium is tetravalent may besubstituted in Examples III and IV without materially changing theprocesses disclosed.

It is also possible to carry out the same reactions (with little or nochange in the reaction conditions) between complex halides of thepolyvalent transition metals and complex sulfides of the transitionmetals to produce lower valent simple or complex halides of the metalsfrom which the metals themselves may be recovered by a fused saltelectrolysis in the manner of Examples V, VI and VII, above.

Accordingly, in the following claims the terms halide and sulfide areintended to include both the simple and complex transition metal halidesor sulfides as the case may be, unless designated as one or the other,specifically.

Having now described my invention in accordance with the patentstatutes, what I desire to claim is:

l. The method of producing a metal of the group consisting of vanadium,niobium, tantalum, titanium, zirconium and hafnium by electrolyzing afused salt melt containing a lower valent halide of said metal whichcomprises: bringing a halide vapor of said metal in which the valence ofthe metal is higher than the valence of the metal in the lower valenthalide to be electrolyzed into contact with a sulfide of one of saidmetals in the form of particles at least as fine as about 200 mesh thevalence of the metal in the sulfide being no higher than the valence ofthe metal in the resulting lower valent product, effecting reactionbetween said halide vapor and said solid sulfide by maintaining thereactants at a temperature at least as high as the volatilizationtemperature of said higher valent metal halide but below that at whichthe resulting lower valent metal halide disproportionates to the metalitself, recovering the lower valent transition metal halide from thereaction mass by extracting same with at least one molten alkali metalhalide, and electrolyzing the molten product containing the recoveredlower valent transition metal halide whereby the transition metal isobtained as a cathode deposit.

v2. Themethod of produch gametal of the group consisting ,of vanadium,niobium, tantalum, titanium, zirconium .andhafnium by electrolyzing afused salt melt containing a lower valent halide of said metal whichcomprises: bringing a higher valent halide of said metal in the vaporstate into contact with a sulfide of one of .said metals in theform ofparticles at least as fine as about 200 mesh, the valence of themetal insaid halide being higher than the valence of the metal in thelowervalent halide to-be electrolyzed and the valence of the metal in thesulfide being no higher than the valence of the metal ,in the resultinglower valent halide product, efiectingreaction between said halide andsaid sulfide at subatmospheric pressure by maintaining the reactants ata temperature at least as high as the volatilization temperature of saidhigher .valent'metal halide but below that atwhich .the resulting'lowermetal halide disproportionates to the metal itself at saidsubatmospheric pressure, recovering the lower valent transition metalhalide from the reaction mass by extracting same with at least onemolten alkali metal halide, and electrolyzing the molten productcontaining the recovered lower valent transition metal halide wherebythe transition metal is obtained as a cathode deposit.

3. The method of producing a metal of the group consisting of vanadium,niobium, tantalum, titanium, Zirconium and hafnium by electrolyzing afused salt melt containing a lower valent chloride of said metal whichcomprises: bringing a higher valent chloride of said metal in the vaporstate into contact with a sulfide of one of .of said metals in the formof particles at least as fine as about 200 mesh, the valence of themetal in said chloride being higher than the valence of the metal insaid lower valent chloride to be electrolyzed and the valence of themetal in the sulfide being no higher than the valence of the metal inthe resulting lower valent chloride product. effecting reaction betweensaid halide and said sulfide by maintaining the reactants at atemperature at least as high as the volatilization temperature of saidhigher valent metal halide but below that at which the resulting lowervalent metal halide disproportionates to the metal itself, recoveringthe lower valent transition metal halide from the reaction mass byextracting same with at least one molten alkali metal halide, andelectrolyzing the molten product containing the recovered lower valenttransition metal halide whereby the transition metal is obtained as acathode deposit.

4. The method of producing titanium which comprises: bringing titaniumtetrachloride in the vapor state into contact with a sulfide of titaniumin the form of particles at least as fine as about 200 mesh, effectingreaction between said tetrachloride and said sulfide by maintaining thereactants at a temperature at least as high as the volatilizationtemperature of said tetrachloride but below that at which the resultingdiand tri-chlorides disproportionate to the metal itself, recovering thediand tri-chlorides from the reaction mass by extracting same with atleast one molten alkali metal halide, and eiectrolyzing the moltenproduct containing the recovered titanium chloride whereby thetransition metal is obtained as a cathode deposit.

5 The method of producing titanium which comprises: bringing titaniumtetrachloride vapor into contact with a sulfide of titanium in the formof particles at least as fine as about 200 mesh, elfecting reactionbetween said vapor and said sulfide at subatmospheric pressure bymaintaining the reactants at a temperature at least as high as thevolatilization temperature of said tetrachloride but below that at whichthe resulting diand tri-chlorides disproportionate to the metal itselfat said subatmospheric pressure, recovering the diand trichlorides fromthe reaction mass by extracting same with at least one molten alkalimetal halide, and electrolyzing the molten product containing therecovered titanium chloride whereby the transition metal is obtained asa cathode deposit,

6. The method of producing titanium which comprises: bringing atetrahalide of titanium in the vapor state into contact with atitaniurinsulfide of the group consisting of titanium monosulfide andtitanium esquisulfide in-the form of particles at least as fine as about200mesh, effecting reaction between said vapor and said sulfide bymaintaining the reactants at a temperature at least as high as thevolatilization temperature'of said tetrahalide but below that at whichthe resulting diand tri-halides disproportionate to the metal itself,recovering the diand tri-halides from the reaction mass by extractingsame with at least one molten alkali metal halide, and electrolyzing themolten product containing the recovered diand tri-halides whereby thetransition metal is obtained as a cathode deposit.

7. The method of producing titanium which comprises: bringing titaniumtetrachloride vapor into contact with 8 a titanium of the groupconsisting of titanium monosulfide and titanium sesiquisulfide in theform of particles at least as fine as about 200 mesh, effecting reactionbetween said tetrachloride and said sulfide at subatmospheric pressureby maintaining the reactants at a temperature'at least as high as thevolatilization temperature of said tetrachloride but below that at whichthe resulting diand tri-halides disproportionate to the metalitself atsaid subatmospheric pressure, recovering the diand trihalides from thereaction mass by extracting same with molten sodium chloride, andelectrolyzing the molten product containing the recovered lower valenttitanium halide whereby the transition metal is obtained as a cathodedeposit. a

No references cited.

1. THE METHOD OF PRODUCING A METAL OF THE GROUP CONSISTING OF VANADIUM,NIOBIUM, TANTALUM, TITANIUM, ZIRCONIUM AND HAFNIUM BY ELECTROLYZING AFUSED SALT MELT CONTAINING A LOWER VALENT HALIDE OF SAID METAL WHICHCOMPRISES: BRINGING A HALIDE VAPOR OF SAID METAL IN WHICH THE VALENCE OFTHE METAL IS HIGHER THAN THE VALENCE OF THE METAL IN THE LOWER VALENTHALIDE TO BE ELECTROLYZED INTO CONTACT WITH A SULFIDE OF ONE OF SAIDMETALS IN THE FROM OF PARTICLES AT LEAST AS FINE AS ABOUT 200 MESH THEVALENCE OF THE METAL IN THE SULFIDE BEING NO HIGHER THAN THE VALENCE OFTHE METAL IN THE RESULTING LOWER VALENT PRODUCT, EFFECTING REACTIONBETWEEN SAID HALIDE VAPOR AND SAID SOLID SULFIDE BY MAINTAINING THEREACTANTS AT A TEMPRATURE AT LEAST AS HIGH AS THE VOLATILIZATIONTEMPERATURE OF SAID HIGHER VALENT METAL HALIDE BUT BELOW THAT AT WHICHTHE RESULTING LOWER VALENT METAL HALIDE DISPROPORTIONATES TO THE METALITSELF, RECOVERING THE LOWER VALENT TRANSITION METAL HALIDE FROM THEREACTION MASS BY EXCTRACTING SAME WITH AT LEAST ONE MOLTEN ALKALI METALHALIDE, AND ELECTROLYZING THE MOLTEN PRODUCT CONTAINING THE RECOVEREDLOWER VALENT TRANSITION METAL HALIDE WHEREBY THE TRANSITION METAL ISOBTAINED AS A CATHODE DEPOSIT.